An internal combustion engine includes at least one combustion chamber formed by a cylinder and capped by a cylinder head. A piston disposed within the combustion chamber is moved toward the cylinder head to compress a mixture of fuel (e.g., gasoline) and air in what is known as a compression stroke of a combustion cycle. A spark plug is then energized to ignite the fuel/air mixture and produce an expanding flame front within the combustion chamber. The ignition of the mixture increases a gas pressure within the combustion chamber and forces the piston away from the cylinder head in what is known as a power stroke or expansion stroke of the combustion cycle.
During conditions in which a combustion chamber temperature is excessively high and/or a pressure of gases within the combustion chamber is excessively high (e.g., higher than standard operating temperature/pressure ranges), a portion of the fuel/air mixture may ignite after discharging a spark via the spark plug during a single combustion cycle and outside of the flame front produced by the spark plug in what is commonly referred to as detonation or knock. Knock results in a localized sharp increase in pressure within the combustion chamber at the location of the portion of detonating fuel/air mixture. The increased pressure may result in engine degradation via mechanical erosion of engine components.
Attempts to address increased combustion chamber pressures include utilizing a pressure-reactive piston within the combustion chamber in order to temporarily increase a volume of the combustion chamber in response to pressure increases. One example approach is shown by Galvin in U.S. Pat. No. 6,907,849. Therein, a piston is disclosed incorporating a bellows spring acting between the piston and an associated connecting rod so as to bias the connecting rod away from a crown of the piston. Another example approach is shown by Youngblood in U.S. Pat. No. 4,376,429. Therein, a method is disclosed for individually controlling a spark timing of engine cylinders in order to increase a performance of each cylinder. Cylinder to cylinder variations in operating characteristics and ambient conditions can be taken into account while selecting a cylinder spark timing for increased torque and reduced knock.
However, the inventors herein have recognized potential issues with such systems. As one example, a bellows spring of an engine piston configured to store energy from combustion of an air/fuel mixture within a combustion chamber, such as that disclosed in the '849 patent referenced above, may result in a decreased torque output of the engine due to compression and expansion of the bellows spring occurring at times during the combustion cycle that result in less force transmitted to the crankshaft by the piston. As another example, methods to reduce engine knock by adjusting ignition timing, such as the method disclosed in the '429 patent referenced above, do not account for a behavior of a pressure-reactive piston within an engine combustion chamber. Because a pressure-reactive piston may decrease a compression ratio of the combustion chamber during operating conditions in which a pressure of gases within the combustion chamber is higher, a likelihood of knock may be reduced. Adjusting the ignition timing in response to knock without additionally adjusting in response to operating conditions of the pressure-reactive piston may result in an ignition timing that is too advanced or too retarded, thereby leading to reduced engine efficiency and potential engine degradation.
In one example, the issues described above may be addressed by a method comprising: estimating a biasing force of a pressure-reactive piston disposed within a combustion chamber of an engine; and adjusting an operating parameter of the engine based on the estimated biasing force. In this way, the estimated biasing force of the piston may be utilized by a controller of the engine in order to adjust engine operation and increase engine performance and/or efficiency.
As one example, an ignition timing of the engine may be adjusted in response to the estimated biasing force. The ignition timing may be advanced or retarded responsive to the estimated biasing force in order to reduce knock within a combustion chamber, for example. The piston may include a sealed base containing a compressible gas with the gas exerting the biasing force against a top wall of the crown of the piston. The controller may estimate the biasing force for different engine operating conditions, such as different piston operating temperatures and different octane ratings of fuel injected into the combustion chamber. By adjusting ignition timing based on the estimated biasing force, an amount of work produced by the engine may be increased and a likelihood of knock may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
FIG. 2 and FIG. 6 are shown to scale, though other relative dimensions may be used if desired.